Apertured film facing and method of making the same

ABSTRACT

An apertured plastic film facing material and method for making the same, together with an improved absorbent product formed therefrom, wherein the edge of the apertures is coated with a hydrophilic material.

This is a division of application Ser. No. 866,830, filed May 22, 1986,now U.S. Pat. No. 4,755,413.

BACKGROUND OF THE INVENTION

The present invention relates to absorbent products which typicallycontain an absorbent core overlaid or overwrapped with a facing or coverlayer.

Apertured plastic films have been used to form the covers or facinglayer of absorbent articles such as disposable diapers, sanitarynapkins, and dressings. The films, being hydrophobic, are not wettedwith body exudates and therefore, provided the exudate passes throughthe apertures of the film facing, the facing will remain clean, ornon-staining, and dry. One difficulty encountered in using aperturedfilms as covers or facings on absorbent products is that body exudatesdo not readily flow through the apertures of the film facing into theabsorbent media. Various approaches have been taken to overcome thisdifficulty. In one approach absorbent material such as tissue is placedin close or touching contact with the under surface of the aperturedfilm facing to "pull" the exudate through the film. However, the use ofa tissue backing can contribute to strike back, or reverse flow, fromthe absorbent core to the face of the cover. In addition, as tissue maybe stained with body exudate, the use of tissue backing may result inthe stained tissue being visible through the apertures, and staining ofthe aperture edge.

In the apertured film facing of the present invention the edge of theapertures is coated with a hydrophilic material to promote fluidtransfer through the apertures into the absorbent core of the absorbentarticle. Thus the apertured film facing of the present inventionprovides a clean dry facing with improved liquid transfer, avoiding thedisadvantages of the prior art solutions by obviating the need for atissue backing.

Other approaches taken to enhance the fluid transfer of apertured filmfacings involve the careful specification of aperture size andpercentage open area of the film. U.S. Pat. No. 2,992,644 discloses anabsorbent dressing with an apertured film facing with a preferredapertured size of from 0.01 to 0.2 inches in equivalent hydraulicdiameter and an open area of from 10 to 40%, with a preferred thicknessof less than one mil. U.S. Pat. No. 4,324,246 describes an absorbentarticle with an apertured film facing having an open area of equal to orgreater than 35%, and wherein at least 75% of the apertures have anequivalent hydraulic diameter equal to or greater than 0.025 inches, andhaving a thickness of less than 0.030 inches.

There are many processes for aperturing plastic film. U.S. Pat. Nos.3,355,974, 3,719,736, 3,682,028, 3,526,349, 3,707,102 and 4,278,871disclose processes for pin perforating plastic films. In the processesdescribed therein, the aperture is not die cut, but is formed as the pinpierces the film, leaving a flap or flashing around the opening.

In the method of the present invention pins are used to aperture thefilm, and to apply a hydrophilic material to the edge of the apertures.U.S. Pat. No. 1,978,620 describes a method wherein, fibrous webs arepierced with needles, the needles dipped into a binder material, andremoved from the web depositing the binder material on the web so as tobond the fibers around the formed hole.

Copending application, now U.S. Pat. No. 4,690,679 describes anabsorbent product with an apertured plastic film facing made from abi-layer film. In the aperturing process the edge of the aperturebecomes formed of the plastic composition of the top, or uppermostlayer.

SUMMARY OF THE INVENTION

The present invention comprises an apertured plastic film facingmaterial for an improved absorbent product, and the method of making thesame, wherein the edge of the apertures is coated with hydrophilicmaterial to promote fluid transfer through the facing to the absorbentcore of the absorbent product. The present invention encompasses the useof any soft, supple hydrophobic plastic film. The apertures formedtherein preferably have an equivalent hydraulic diameter of at least0.025 inches. The distance between apertures is equal to or greater than20% of the equivalent hydraulic diameter.

With the facing of the present invention, fluid transfer need not beregulated strictly by the size and/or configuration of the apertures, asthe fluid transfer therethrough is enhanced by the coating ofhydrophilic material. In addition, as mentioned above, a tissue backingor other means to draw fluid through the apertures is not needed,allowing greater latitude in the construction of an absorbent productutilizing the facing of the present invention. Lastly, the facingmaterial of the present invention provides an absorbent product with acleaner, dryer surface due to the hydrophilic coating of the apertures.In addition, the facing of the present invention provides a more opaquecover for an absorbent product in that smaller aperture sizes can beused while achieving fluid flow of larger apertures, by the use of thehydrophilic coating of the apertures, so that less of the underlyingstain in the absorbent core is visible through the cover.

According to the method of the present invention a supply of film isbrought into pressure contact with a the plurality of pins, or needleswhich are caused to extend through the film and are then withdrawn fromthe film leaving the apertures. To apply the hydrophilic material to theedges of the apertures, the hydrophilic material may be coated on thepins prior to contacting the film with the pins, or the pins may becoated with hydrophilic material as they extend through the film, thecoating being applied as the pins are withdrawn from the film.

In an alternate embodiment utilizing hollow needles, the hydrophilicmaterial may be supplied through a hollow in the needle to a port at thetip of the needle, to coat the edge of the aperture as the needlespierce the film and/or when they are removed therefrom.

In another preferred embodiment, the pins or needles are heated tofacilitate aperturing of the film and to permit the use of moltenhydrophilic material. In a still preferred embodiment the pins orneedles are heated to a temperature above the softening point but belowthe melting point of the film so as to avoid shrink back of the filmfrom the pins or needles. Indeed, when the hydrophilic material is to bedeposited in the apertures as the pins are removed from the film, it isessential that the temperature of the pins or needles be maintainedbelow the melt point of the film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a method for practicing thepresent invention.

FIG. 2 is an enlarged side view, in partial cross section, of a hollowneedle which may be used to practice the method of the presentinvention.

FIG. 3 is a perspective view of an improved absorbent product inaccordance with the present invention.

FIG. 4 is a cross-sectional view of the sanitary napkin of FIG. 3.

FIGS. 5 and 6 are cross-sectional views of sanitary napkins constructedusing alternate techniques in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises an apertured film facing material, and amethod for making the same, wherein the apertures are coated with ahydrophilic material, and an improved absorbent product utilizing saidfacing. The hydrophilic material used to coat the edge of the aperturesmay be any known hydrophilic material suitable for use on an absorbentproduct, for example, hot water soluble polyvinyl alcohol, glycerine,guar gum, or hydroxyethylcellulose. The film used to make the facing ofthe present invention is a thin hydrophobic plastic film and may be, forexample, a polyolefin, a vinyl, or an acrylic film. In a preferredembodiment the plastic of the film be compounded with titanium dioxideso as to enhance the opacity of the film. Opacity of the facing isdesirable to "hide" the underlying absorbent core, especially oncestained. In another preferred embodiment, the film should have athickness in the range of 0.5 to 1.5 mils. If the film is too thin itwill have insufficient strength when perforated to be used as a facingfor an absorbent product. If the film is too thick it will be too stiffand non-conformable to be used as a facing for an absorbent product. Inthe most preferred embodiment, the apertured facing of the presentinvention is made from a one mil low density polyethylene film.

The apertures of the facing of the present invention preferably have anequivalent hydraulic diameter of at least 0.025 inches. The aperturesmay be larger, and may vary in size, and configuration. At equivalenthydraulic diameters of 0.05 inches or more, apertured plastic filmfacings exhibit strike back or reverse flow of the fluid from theabsorbent core to the outer surface of the facing. As the hole size isreduced, fluid strike back is reduced. In the invention of the presentapplication wherein the apertures are coated with hydrophilic material,to promote fluid flow through the apertures, rapid fluid transferthrough the facing material can be achieved at smaller hole sizes thanwith uncoated apertures.

The percentage open area of the facing should be sufficient to allowcomplete transfer of the fluid through the facing so as to leave a cleandry surface on the facing. Generally, open areas of greater than 35% areused. As thin films are used to form the apertured facing of the presentinvention, too great an open area can reduce the strength of the film tothe point where it is no longer acceptable as a facing material. Ingeneral the distance between apertures should be equal to or greaterthan 20% of the equivalent hydraulic diameter of the apertures tomaintain adequate strength in the facing material. Good results havebeen achieved in the facing of the present invention with 150 holes persquare inch on 0.056 inch centers yielding a 37% open area. Good resultswere also achieved with the facing of the present invention having 195holes per square inch on 0.048 inch centers, yielding a 35% open area.

The method of the present invention will be described in relation toFIG. 1. According to the method of the present invention, a hydrophobicplastic film sheet 1 is supplied and placed in pressure contact withpins 3. The pins are provided on a rotatable roll 4 so as to provide acontinuous process. In the apparatus depicted in FIG. 1 the pressurecontact is achieved through the use of guide rolls 2 and 6 which are notin alignment with (e.g. the surfaces of which do not fall in a straightline with) the surface of the pins. The pressure contact of the pinswith the film, caused by the offset of the pins and the carrier rolls,causes the pins to puncture the film and extend therethrough formingapertures in the film. As shown in FIG. 1 a hydrophilic agent may beapplied to the ends of the pins by e.g., dipping the ends of the pinsinto a bath 5 of hydrophilic solution while the pins extend through thefilm. As the film moves away towards carrier roll 6, the pins arewithdrawn from the film and the edges of the apertures are coated with ahydrophilic material.

In another embodiment of the method of the present invention, thehydrophilic agent may be applied to the pins prior to placing the pinsin pressure contact with the film. In this embodiment the edges of theapertures are coated with hydrophilic material as the pins puncture thefilm. In this embodiment or the embodiment depicted in FIG. 1, thehydrophilic material may be applied to the pins by kiss coating the pinswith a brush, sponge, or fabric to which hydrophilic material has beenadded.

In an alternative embodiment, the pins may be provided along a flatsurface which is raised and lowered along a line tangential to the film,to bring the pins into pressure contact with the film, and cause thepins to puncture the film and extend therethrough, forming apertures inthe film.

In another alternative embodiment the pins may comprise hollow needlessuch as the hollow needle as shown in FIG. 2. The hollow needle 7 haschannel 8 for delivering the hydrophilic material to the tip of theneedle, through the port 9 located at the tip of the needle.

In perforating the plastic film, the pins or needles may be heated so asto make a smoother aperture in the film. When heating the pins orneedles it is preferred to maintain the temperature thereof above thesoftening point but below the melt point of the film. If the temperatureis above the melt point of the film, the film will shrink back from thepin, which may cause an uneven surface or surface roughness which isunacceptable in a facing material. In addition, in those embodiments ofthe method of the present invention where the hydrophilic material wasapplied to the pins as the pins pierce and extend through the film, itis necessary to keep the temperature of the pins below the melt point ofthe film because if the film shrinks away from the pins, it is difficultto reverse coat the edge of the apertures as the pins are withdrawn fromthe film. With certain films and particularly with very thin films, itmay be necessary to carry the film through the process on a releasepaper in order to facilitate removal from the pins. The preferredembodiment of the method of the present invention utilizes a 1 mil, lowdensity polyethylene film and a pin temperature of 110° C.

The apertured film facing material of the present invention may be usedto form an improved absorbent product such as that shown at 10 in FIGS.3 to 6. The absorbent product comprises an absorbent core 11 havingfirst and second opposed faces, 12 and 13 respectively. A liquidimpermeable back sheet 14 overlies the first opposed face of theabsorbent core and a liquid permeable top sheet 15 overlies the secondopposed face of the absorbent core. The liquid permeable top sheetcomprises a hydrophobic film having a multiplicity of apertures 16therein, the edge of the apertures being coated with hydrophilicmaterial to promote fluid transfer through the apertures into theabsorbent core.

The use of the facing of the present invention provides an improvedabsorbent product with a cleaner, drier appearance and feel. The coatingof the apertures with hydrophilic material promotes fluid transferthrough the facing into the absorbent core, leaving the surface 17cleaner and drier. In addition, by coating the apertures to providebetter fluid transfer therethrough, smaller apertures may be used toachieve the fluid transfer of larger uncoated apertures, while providingbetter opacity or cover of the underlying absorbent core, especiallywhen stained. Further the coating of the edge of the apertures allowsthe use of apertures of varying configuration, such as a diamond shape,which may be formed by pins or needles of a diamond shapedcross-section.

The absorbent core 11 is sealed between the liquid impermeable backsheet14 and the liquid permeable top sheet 15 in a manner describedhereinbelow. The absorbent core 11 may be comprised of any of the wellknown absorbents such as wood pulp, rayon, synethtic absorbents in theform of fibers, powder, or foam or combinations thereof. Absorbencyenhancers such as the so called "superabsorbent" materials may beemployed. Non-hydrophilic materials may also be employed in combinationwith absorbent materials. One such example is a low density, thermalbonded non-woven fabric comprising a mixture of absorbent fibers andstaple length polyester/polyethlene conjugate thermoplastic fibers. Theabsorbent fibers may be wood pulp or other cellulosic fibers which mayhave been treated to enhance absorbency. Suitable conjugate fibers arefibers which comprise a polyester core surrounded by a sheath ofpolyethylene. A highly satisfactory absorbent core is produced by athermally bonded absorbent fabric comprising 54% by weight of wood pulpfibers and 46% by weight of conjugate fibers having a staple length of3.81 centimeters and a denier of 3.0. The fabric is stabilized bypassing hot air through the fibers and thereby melting the polyethylenewhich bonds the fibers together upon cooling. Such a fabric is capableof holding about seventeen times its own weight of distilled water.Alternatively, an absorbent batt of densified web material may beemployed, as described in U.S. Pat. No. 4,551,142.

The fluid impermeable backsheet 14 acts as a barrier to body fluids andprevents staining of the undergarments of the user. The backsheet maycomprise any thin, flexible body fluid impermeable material such as apolymeric film, e.g., polyethylene, polypropylene, or cellophane.Alternatively the barrier may comprise a normally fluid perviousmaterial that has been treated to be impervious such as impregnatedfluid repellant paper. If desired, the backsheet 14 may be adhesivelyaffixed to the garment facing side of the absorbent batt 11.

Disposed on the garment facing side of the backsheet 14 arelongitudinally extending pressure sensitive adhesive means 18 providedfor attaching the napkin to the crotch portion of an undergarment. Whilesuch adhesive means are illustrated in the form of longitudinallyextending lines, it will be understood that various patterns such asspots or transverse lines are suitable. The adhesive employed may be anyof the large number of pressure sensitive adhesives that arecommercially available, including water based adhesives such as acrylateadhesives, e.g., vinyl acetate/2-ethyl-hexyl acrylate copolymer whichmay be combined with tackifiers. Alternatively the adhesive may alsocomprise a pressure sensitive rapid setting hot melt adhesive. Theadhesive element may also comprise a double faced tape.

Overlying the adhesive means 18 is a protective release strip 19 whichis provided to protect the adhesive means from dirt and unintendedadhesion prior to use. The release strip 19 may be constructed of anysuitable sheet-like material which adheres with sufficient tenacity tothe adhesive means to remain in place prior to use but which can bereadily removed when the napkin is to be used. A particularly usefulmaterial is a semi-bleached kraft paper, the adhesive contacting side ofwhich has been silicone treated to provide easy release from theadhesive means 18.

As seen in FIGS. 3 and 4 the liquid permeable top sheet 15 may bethermally bonded to the backsheet 14 about the periphery 20 of theabsorbent product 10. In FIGS. 3 and 4 the bonded periphery 20 is seento be outwardly extending from the absorbent product. Alternatively thebacksheet 14 may be folded upward around the edges of the absorbent core11, and the top sheet 15 folded over the back sheet edges and thermallybonded at the overlap 21 as shown in FIG. 5. This technique gives theedges of the napkin a more rounded and comfortable appearance. In otherabsorbent product applications it may be desirable to completely enclosethe absorbent core 11 in an apertued film cover as shown in FIG. 6. Inthis embodiment the top sheet 15 surrounds the absorbent core 11 and theback sheet 14, with the edges of the top sheet adjoining each other at aseam indicated at 22. On either side of the seam the cover formed by thetop sheet is thermally bonded to the underlying back sheet 14, asindicated at 23 and 24. At the longitudinal ends of the napkin theproduct may be sealed by thermal bonding the edge of the body facingside of the cover to the edge of the garment facing side of the cover.

What is claimed is:
 1. An improved disposable absorbent articlecomprising:an absorbent core means for absorbing liquid, said absorbentcore means having a first and a second opposed face; a liquidimpermeable backsheet overlaying said first opposed face of saidabsorbent core; and a liquid permeable topsheet overlaying said opposedface of said absorbent core means, said topsheet being a hydrophobicfilm having a multiplicity of apertures therethrough, the edge of saidapertures being coated with a hydrophilic material.
 2. The disposableabsorbent product of claim 1 wherein the distance between the aperturesof the top sheets is greater than about 20% of the diameter of theapertures.
 3. The disposable absorbent product of claim 2 wherein saidapertures have an equivalent hydraulic diameter of 0.025 inches or more.4. The disposable absorbent product of claim 1 wherein said topsheet hasa thickness of about 0.5 to 1.5 mils.
 5. The disposable absorbentproduct of claim 1 wherein the distance between apertures is equal to orgreater than 20% of the equivalent hydraulic diameter of the apertures.6. The disposable absorbent product of claim 1 wherein the hydrophobicfilm is a 1 mil, low density polyethylene film.
 7. The disposableabsorbent product of claim 1 comprising a sanitary napkin.
 8. Thedisposable absorbent product of claim 1 comprising a diaper.